Liquid salts of imidazole compounds have ionic conductivity, flame retardance, non-volatility, high polarity and solubility, and by making use of these properties, are expected to be ionic liquids having various functions useful for electrolytes for fuel cell, secondary battery, capacitor, dye-sensitized solar cell and electrochromic device, or reaction media, catalyst, and chemical separation and reprocessing of nuclear fuel.
For example, JP2003-62467A discloses an ionic liquid composition containing 1-(2,2,2-trifluoroethyl)-3-methylimidazolium trifluoromethanesulfonate. This salt of an imidazole compound is prepared by allowing 1-(methoxyethyl)-3-methylimidazolium trifluoromethanesulfonate to react with trifluoromethanesulfonic anhydride in the presence of trifluoroethanol and pyridine as disclosed in P. Bonhote et al., Inorganic Chemistry, 35, pp. 1168-1178 (1996). However in this preparation process, separation of impurities derived from unreacted imidazolium salt is difficult, and in addition, an expensive reacting agent is used and yield is as low as about 28%. Also in the structure of this imidazolium salt, a fluorine-containing alkyl group is not introduced directly on nitrogen, and an effect of increasing cations for use as a Lewis acid catalyst is difficult to obtain.
V. V. Rudyuk et al., J. Fluorine Chem., 125, pp. 1465-1471 (2004) discloses that after conversion of an imidazole compound into a potassium salt, when the potassium salt is allowed to react with CF2═CFCl under refluxing in dimethylacetamide, an imidazole compound in which N—K groups of the imidazole compound have been converted to N—CF═CFCl groups and N—CF2CFCl groups can be obtained, and yield of the imidazole compound having N—CF2CFCl groups is 20 to 85%, and also discloses that when an imidazole compound is allowed to react directly with CF2═CF2 in tetrahydrofuran in the presence of a catalytic amount of metallic potassium, an imidazole compound in which N—H groups of the imidazole compound have been converted to N—CF2CFH groups can be obtained at yield of 68%.
D. C. England et al., J. Am. Chem. Soc., 82, pp. 5116-5122 (1960) and U.S. Pat. No. 2,861,990 disclose that a pyrrole compound or an indole compound is allowed to react with fluoroalkene such as CF2═CF2, CF2═CFCl or CF2═CFCF3 in the presence of metallic potassium or metallic sodium, and a pyrrole compound or an indole compound in which a N—H group of the pyrrole compound or the indole compound has been added to the fluoroalkene can be obtained at yield of 60 to 88%.
Alkali metals described in these V. V. Rudyuk et al., J. Fluorine Chem., 125, pp. 1465-1471 (2004), D. C. England et al., J. Am. Chem. Soc., 82, pp. 5116-5122 (1960) and U.S. Pat. No. 2,861,990 are substances which are so easily reactable with water, and handling thereof is not easy because water control of all chemicals to be used in the reaction and water control in working environment are necessary. In addition, in these processes, a step for removing alkali metal salt produced after the reaction is required.
Further, for ionization of an obtained imidazole compound having a fluoroalkyl group, there is employed a method of anion exchange by substitution reaction of the compound with methyl iodide as disclosed in Y. L. Yagupolskii et al., J. Fluorine Chem., 126, pp. 669-672 (2005).